Inkjet ink, inkjet printing process and ink set for forming an image on a substrate and aqueous pigment dispersion for forming the inkjet ink

ABSTRACT

Inkjet ink for forming an image on a substrate includes a pigment P, a block copolymer dispersant D for dispersing the pigment P, and an aqueous carrier. The block copolymer dispersant D includes an anchoring segment A for anchoring to the pigment P, where the block copolymer dispersant additionally comprises a matrix stabilization segment M for aqueous phase stabilization of the pigment. The anchoring segment A includes a repeating unit R1 and a repeating unit R2, different from R1, where the repeating unit R1 is less hydrophobic than the repeating unit R2, the repeating unit R1 includes a (poly)alkylene oxide coupled to a terminal group via a direct bond, a —C—O—C— ether bond or a —C—O—(C═O)—N— urethane bond, and the terminal group is selected from an alkyl group, an aryl group and combinations thereof.

FIELD OF INVENTION

The field of the invention relates to an inkjet ink, an inkjet printingprocess and ink set of inkjet inks for forming an image on a substrateand aqueous pigment dispersion for forming the inkjet ink. The inkjetprinting process for forming an image on a substrate uses an inkjet inkaccording to the present invention. The ink set of inkjet inks forforming an image on a substrate comprises an inkjet ink according to thepresent invention. The field of the invention further relates to anaqueous pigment dispersion for forming the inkjet ink according to theinvention.

BACKGROUND

An inkjet printing process for forming an image on a substrate byapplying a plurality of inkjet inks on the substrate is generally known.Inkjet inks for industrial printing applications primarily use pigmentsas colorants, except in the textile industry which often still usesreactive dye based inkjet inks. Pigments are solid materials that alsoremain as a solid in the inkjet ink carrier, in contrast to dyes whichactually dissolve in the carrier medium. The pigment particles arefinely dispersed in an ink and are of nanometer scale size. A typicalinkjet printing process uses 3 or 4 colors of inkjet inks to createmulticolor images. Typical colors are cyan (C), magenta (M), yellow (Y)and black (K). The CMY color inkjet inks are typically made up oforganic pigments, wherein some contain a metal atom in a complex,whereas the K inks use organic pigments typically made of carbon black.The pigment powders are commercially not available as nanometerparticles, but come as agglomerates and aggregates of pigment particlesformed during the synthesis process. The agglomerates and aggregates ofpigments need to be made smaller and will typically be brought to thenanometer scale size by grinding, milling, or other techniques to breakup the agglomerates and aggregates. The particle size reduction of thepigment powder particles is often carried out in a carrier medium thatwill be used in a later stage in the ink. Such a process step of makingpigment particles smaller is often done at higher pigment concentrationthan in the final ink and is then referred to as the pigment dispersion.

As discussed above, the pigments are mechanically broken down to sizesof 30-300 nm which are needed to be stabilized by adding dispersingagents (or surfactants) to physically and/or electrostatically preventthe pigments to re-agglomerate. Typically this is a physico-chemicalphenomenon as there is no chemical bond between the pigment surface andthe dispersing agent, which can be polymeric dispersing agents (e.g.random copolymer, block copolymers, grafted copolymers) or surfactants.

Sometimes also covalently bound chemicals can be used for pigmentparticle stabilization in water based inks, but requires mostly anexpensive production process.

A known approach for making pigment dispersions is based on randompolymerized dispersing agents: they are used in analog inks e g forflexographic printing, but also in inkjet inks Typically, the randompolymers are built up of two kinds of monomers, one which is morepigmentophilic and another which is more compatible with the carrierliquid or matrixophilic so to speak. These monomers are randomly spreadout in the polymer, so no polymer structure (i.e. monomer sequence) andno number of monomeric repeating units is pre-defined. Hence a number ofpolymers will have a favorable structure, capable of stabilizing pigmentparticles in the liquid, but there is a non-active population as wellhaving a “bad” structure for stabilization (e.g. not enough pigmentanchors, not close enough to each other pigment anchors, too fewmatrixophilic groups). These fractions often are not adsorbed or readilydesorbed yielding in a non-stable dispersion. Two of the main problemsare that the not-absorbed high molecular weight dispersant molecules arepresent in the matrix and therefore contribute to a higher dispersionviscosity. Additionally visco-elastic properties of the final ink may beaffected negatively. Both effects of increased viscosity and affectedvisco-elastic properties of the final ink may disturb the drop formingprocess, such as by increased mist forming.

Another known approach is block copolymer dispersants. Block copolymerdispersants containing hydrophobic and hydrophilic block segments havebeen disclosed in numerous inkjet ink patents. U.S. Pat. No. 5,859,113(DU PONT) discloses an AB block copolymer dispersant with a polymeric Asegment and a polymeric B segment.

A wide variety of polymeric dispersants, such as block copolymerdispersants, has been proposed, but the dispersion stability ofpigments, especially in inkjet, still needs further improvement.

For consistent image quality, the inkjet ink requires a dispersionstability capable of dealing with e.g. high temperatures (above 60° C.)during transport or storage of the ink to a customer and changes in thedispersion medium of the inkjet ink during use such as evaporation ofwater and increasing concentrations of water soluble organic solvents orthe addition of functional polymers to improve the adhesion, drying,water or scratch resistance of the ink on a substrate.

In industrial inkjet processes the demands for stability of pigmentdispersions usable for inkjet printing is also increasing, in particularat higher jetting frequencies, smaller droplet formation, higher jettingtemperatures and/or more demanding single pass printing applications.

All the ink additives (such as surfactants, latexes, polymers,oligomers, (water soluble) organic solvents) can compete with thedispersing agents to interact with the pigment surface and thusnegatively influence the pigment dispersion stability. These additivesare typically organic in nature (to certain extent even incompatiblewith the ink matrix), and they will compete for the same organic surfaceof the pigments, especially pronounced in water based inks. If thisoccurs inside the printhead, it will lead to removal of the dispersingagent from the surface, lowering or destroying the stability and giverise to irreversibly blocked nozzles resulting in e.g. white lines andsevere reduction of image quality or inks containing too large particlesthat negatively influence the ink flow into the head.

Due to the increasing demands, there is a need to further optimize theink additives, such as optimization depending on the type of colorpigment, to obtain a consistent image quality and a reliable inkjetprocess.

In addition, for some color pigments it has found to be more difficultto obtain fine pigment dispersions in a simple way e.g. using a millingprocess, while enhancing the pigment stability required for an inkjetink.

A desire remains to formulate block copolymer dispersing agents, whichprovide a high degree of milling performance (i.e. able to mill downvery easy to the desired particle size) for different pigments withoutthe need of additional co-solvents and keeping a high level of stabilityof the pigment dispersion such that the obtained pigment dispersionsprovide a broad versatility for formulating final inkjet inks.

As such, there is a need to be able to manufacture such stable pigmentedinkjet inks, wherein a dispersion stability of the pigment in the inkjetinks may be enhanced easily for a wider diversity of inkjet inks.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided an inkjetink for forming an image on a substrate, the inkjet ink comprising apigment P, a block copolymer dispersant D for dispersing the pigment P,and an aqueous carrier; wherein said block copolymer dispersant Dcomprises an anchoring segment A for anchoring to the pigment P, whereinthe block copolymer dispersant additionally comprises a matrixstabilization segment M for aqueous phase stabilization of the pigment,wherein the anchoring segment A comprises a repeating unit R1 and arepeating unit R2, different from R1, wherein the repeating unit R1 isless hydrophobic than the repeating unit R2, wherein the repeating unitR1 comprises a (poly)alkylene oxide coupled to a terminal group via adirect bond, a —C—O—C— ether bond or a —C—O—(C═O)—N— urethane bond,wherein the terminal group is selected from an alkyl group, an arylgroup and combinations thereof. In particular the repeating unit R1comprises a (poly)alkylene oxide coupled to a terminal group via adirect bond, or a —C—O—(C═O)—N— urethane bond.

According to another aspect of the invention there is provided an inkjetprinting process for forming an image on a substrate by applying aplurality of inkjet inks on the substrate, wherein the plurality ofinkjet inks comprises an inkjet ink according to the invention.

According to another aspect of the invention there is provided an inkjetink set comprising a plurality of colored inks, wherein at least one ofthe inks is an inkjet ink according to the invention.

According to another aspect of the invention there is provided an inkjetprinter responsive to digital data signals, which has been equipped withan inkjet ink according to the invention or inkjet ink set according toinvention.

According to another aspect of the invention there is provided anaqueous pigment dispersion for forming an inkjet ink, the pigmentdispersion comprising a pigment P, a block copolymer dispersant D fordispersing the pigment P, and an aqueous carrier; wherein said blockcopolymer dispersant D comprises an anchoring segment A for anchoring tothe pigment P, wherein the block copolymer dispersant additionallycomprises a matrix stabilization segment M for aqueous phasestabilization of the pigment, wherein the anchoring segment A comprisesa repeating unit R1 and a repeating unit R2, different from R1, whereinthe repeating unit R1 is less hydrophobic than the repeating unit R2,wherein the repeating unit R1 comprises a (poly)alkylene oxide coupledto a terminal group via a direct bond, a —C—O—C— ether bond or a—C—O—(C═O)—N— urethane bond, wherein the terminal group is selected froman alkyl group, an aryl group and combinations thereof; and wherein theaqueous carrier contains water.

Advantageous Effects of the Invention

It has been found by the inventors that an easy manufacturing of astable pigmented inkjet ink is possible using the block copolymerdispersant D. The block copolymer dispersant D comprises a combinationof a repeating unit R1 and a repeating unit R2, different from R1. Therepeating unit R1 comprises a (poly)alkylene oxide coupled to a terminalgroup via a direct bond, a —C—O—C— ether bond or a —C—O—(C═O)—N—urethane bond, wherein the terminal group is selected from an alkylgroup, an aryl group and combinations thereof.

The repeating unit R1 of the block copolymer dispersant D is lesshydrophobic than the repeating unit R2 of block copolymer dispersant D.The block copolymer dispersant D has been found to improve the pigmentstability required for an inkjet ink and at the same time to enhance aneasy manufacturing of a fine pigment dispersion having fine pigmentparticles in a simple way e.g. using a milling process. The combinationof the repeating unit R1 and the repeating unit R2 surprisingly combinesthese advantages without any adverse effects. Additionally, no orminimal water soluble organic co-solvents are needed to obtain thebeneficial fine pigment particles. As such, the pigment dispersionaccording to the invention can be used in a versatile way to provideinkjet inks having various compositions, such as containing no orvarious amounts of water soluble organic co-solvents.

Pigments may have surfaces present with different hydrophobicity degreesmeaning that one part of the pigment surface can be rather hydrophobicand another part less hydrophobic. It has been found that a verydedicated design/choice of the block copolymer dispersant is necessaryto achieve stable pigment dispersions.

The use of the block copolymer dispersant D having two differingrepeating units R1, R2 in the anchoring segment A for anchoring to thepigment P may seem to increase the complexity of the block copolymerdispersant D, but the flexibility in mixing ratio of different repeatingunits of the block copolymer dispersant results in drastically increasedmilling performance and achieves the manufacture of even more versatileand stable pigment dispersions.

In addition, the selected block copolymer dispersant D for dispersingthe pigment P in the ink may prevent that the pigment P re-agglomeratesin the resulting inkjet ink, even when various ink additives, such aswater soluble organic solvents, which may compete with the dispersants,are added to the inkjet ink.

Moreover the use of block copolymer dispersant D for dispersing thepigment P may support and enhance the jetting stability in industrialinkjet printing having increasing demands for ink durability andconsistent image quality.

(Pigment Dispersion Stability)

A pigment dispersion stability as defined in this application mayinclude a pigment particle grinding characteristic of the pigmentdispersion and may include a pigment dispersion stability characteristicwhen exposed to extreme conditions, such as elevated temperatureconditions (relative to room temperature or a normal operationtemperature of the ink) and critical aqueous carrier conditions, such asby adding and/or increasing the amount of competing water solubleorganic solvents to the carrier and/or other ink additives.

The pigment particle grinding characteristic of the pigment dispersionshows the ability to easily reduce the size of the agglomerates andaggregates of pigments down to nanometer sizes, such as 30-300 nm, whichare stabilized by adding the block copolymer dispersant to physicallyand/or electrostatically prevent the pigments to re-agglomerate.

EMBODIMENTS OF THE INVENTION

The following exemplary embodiments are described, however the presentinvention is not limited to these embodiments:

(Block Copolymer Pigment Dispersant)

It has been found that by selecting the repeating units of the anchoringsegment of the block copolymer dispersant D having different propertiesallows dedicated chemical fine-tuning of the dispersing agent, whichcreates the possibility to optimize the physical interaction of thepolymeric dispersing agent to the pigment surface. The balancing act inthe design of the copolymer dispersant lies in apigmentophilic/matrixophilic balance. For water based inks importantseems the relative hydrophilic/hydrophobic nature of the polymer. Inthis way the pigment particle P may be compatibilized with the carrier.

The inventors have found that only altering the number of repeatingunits in the segments may be insufficient, especially when facingpigments with chemically different areas on the pigment particlesurface. In order to offer a solution for this problem the inventorshave found that it can be highly beneficial to also use a secondchemically different type of repeating unit, possible also with adifferent number of repeating units.

Block copolymer dispersants, unlike random copolymers, have anengineered molecular structure in chemical composition (block-wiseincorporated in the polymer), narrow molecular weight distribution,and/or defined block chain lengths of the different constituting blocksor monomers. Block copolymer dispersant can be built up of two or moredifferent monomers, arranged in blocks in the polymer.

A block of the block copolymer of the present invention has a narrowmolecular weight distribution, and/or defined block chain length. Ablock copolymer is defined by a polymer consisting of different blockswherein each block is substantially equal in size and compositionmeaning that all polymer molecules have substantially the samecomposition and length. The same composition means that, in case theblock contains one type of repeating unit, that the repeating unit isthe same, or, in case the block contains two or more different repeatingunits, that the number ratio between the respective repeating units isthe same.

The fact that the individual blocks, and also the complete polymer, isequal in size can be expressed by the polydispersity PD, defined asMw/M. of the individual block or the complete polymer respectively,which is preferably lower than 1.6, more preferably lower than 1.5.

In an exemplary embodiment, the block copolymer dispersant D has apolydispersity PD lower than 1.6, more preferably lower than 1.5. In aparticular embodiment, each of the blocks of the block copolymerdispersant D has a polydispersity PD lower than 1.6, more preferablylower than 1.5.

Compared to random copolymers that are used commonly as a pigmentdispersing agent, the pigmentophilic monomers in block copolymerdispersants can be built as a block of appropriate size and chemistrynext to one or more matrixophilic monomer-based blocks of appropriatesize and chemistry. This provides options to fine-tune and maximize theinteraction between a certain pigment and a block copolymer baseddispersing agent. A maximized interaction will yield a strongphysico-chemical connection of the dispersing agent with the pigmentsurface. Since dispersing agents are put on the surface of pigments toprevent re-agglomeration of the pigments, this strong fixation of thedispersing agent to the pigment surface may inhibit desorption of thepolymer from the pigment surface, may enable the creation of highlystable pigment dispersions, especially when used in the final ink, andadditionally may provide the advantage of low levels of dispersing agentdissolved in the matrix.

A strong link of dispersing agent with the pigment will withstand alsothe competing interactions of other ink additives that in water basedinks tend to be (at least partly) hydrophobic in nature and thus want toget to the organic pigment surface as well.

In an exemplary embodiment, the block copolymer dispersant D is selectedfrom a diblock copolymer and a triblock copolymer. The matrixstabilization segment may comprise one block formed from one monomer andmay further comprise another block formed from another monomer. Theanchoring segment may comprise one block formed from one monomer and mayfurther comprise another block formed from another monomer. Thus, theblock copolymer dispersant may be a diblock copolymer having two blocks,may be a triblock copolymer having three blocks and may have any othersuitable number of blocks larger than three.

The matrix stabilization segment and the anchoring segment of the blockcopolymer dispersant may be arranged in any order along the blockcopolymer dispersant.

The block copolymer dispersant D has a Mw of 2000 to 20000 g/mol morepreferably between 3000 to 12000 g/mol, wherein the ratio between thetotal number of repeating units of anchoring segment A to the totalnumber of repeating units of stabilizing segment M of D is 0.5 to 10more preferably 1 to 5. When the molecular weight of the dispersant islower than 2000 g/mol the dispersion stability is not maintained andwhen the molecular weight is higher than 20000 g/mol the viscosity ofthe dispersion is often too high or the dispersion stability may beaffected by dispersant polymer chains anchoring to more than one pigmentparticle. Polymeric dispersants with a molecular weight above 2000 g/molalso provide the benefit of adhesion to the substrate during the dryingprocess of the ink, even without the addition of binders. Additionally,the use of analogue or digital overprint varnishes can aid in furtherincreasing the properties of the printed image, e.g. mechanical andchemical resistance, hot scuff resistance, and coefficient of friction.

The acid value of the block copolymer dispersant D is in the range of 50to 250 mg KOH/g polymer more preferably 60-200 mg KOH/g polymer allowinga good solubility in water. The acid value of the block copolymerdispersant D is determined by measuring/calculation the Acid Value (AV)of the block copolymer dispersant D. The acid value is thus a measure ofthe weight ratio between the matrix stabilization segment and anchoringsegment. At a too high AV, meaning that the contribution of the matrixstabilization segment is too high, the polymer dispersant mighttemporarily desorb from the pigment surface affecting e.g. the pigmentdispersion stability.

Another problem of a too high AV is that a water fastness of the inkimage on a substrate could be insufficient.

On the other hand, at a too low AV, when the contribution of theanchoring segment is too high, the solubility of the polymer dispersantcan be insufficient to provide an efficient milling process, especiallywhen milling with low amounts of a co-solvent or even in absence of aco-solvent. Note that the benefit of a dispersion, which issubstantially free of co-solvent is highly preferred as this leaves afree choice of ink components during ink formulation.

Another aspect of acid value is the importance of the value in terms ofinteraction with primers that are typically used for improving imagequality on paper (i.e. uncoated kraft and recycled as well as offsetcoated media) and film substrates. Analogue and digitally appliedprimers are used to achieve lower intercolor bleeding, higher opticaldensity, etc. However, primers typically contain cationic components(polymeric or multivalent metal cations) or acidic components, intendedto reduce or ‘crash’ the stability of the dispersed pigments. Suchprimers work best when the acid value of the pigment dispersion is lowerthan 200 mg KOH/g. To create an optimal bonding between the crashedpigment and the printed substrate such primers often also contain apolymeric binder.

The combination of the above mentioned range of molecular weight andacid value of the block copolymer dispersant D is supportive to preparethe pigment dispersion in an easy and cost effective way, e.g. withoutthe use of solvents which have to be removed afterwards. The combinationmay also support a good interaction with a primer which may be typicallyused in the ink composition, e.g. for printing on uncoated corrugatedboard in order to enhance the colour intensity on uncoated corrugatedboard.

In preferred embodiments, the block copolymer dispersant D is awater-soluble block copolymer dispersant. A block copolymer is definedas “water-soluble” when the block copolymer remains in solution in waterat 25° C. with at least 15 wt. % of dry polymer in water during at leasta week, preferably remains in solution in water at 25° C. for at leastone or more months, more preferably the weight percentage of dissolveddry polymer in water at 25° C. is at least 20 wt. % and most preferablythe weight percentage of dissolved dry polymer in water at 25° C. is atleast 25 wt. % or above.

A block of a block copolymer dispersant according to the invention mayadditionally contain an initiator moiety, a terminating moiety, an endgroup, and/or a linking moiety.

A repeating unit of a block may comprise a substituent. The substituentmay optionally be converted to another substituent, thereby modifyingthe repeating unit, after polymerizing the block or after polymerizingthe block copolymer.

In an exemplary embodiment, the block copolymer dispersant D isconstituted by a linear polymer chain. In another exemplary embodiment,the block copolymer dispersant D is at least partially crosslinked,wherein the block copolymer dispersant is attached to or at leastpartially encapsulates the pigment.

A matrix stabilization segment and a anchoring segment of a blockcopolymer dispersant may be arranged in any order along the blockcopolymer dispersant.

In an exemplary embodiment, the anchoring segment A of the blockcopolymer dispersant D comprises a first anchoring block A1, comprisingthe repeating unit R1, and a second anchoring block A2, comprising therepeating unit R2.

In an exemplary embodiment, the block copolymer dispersant D has atleast three blocks and the matrix stabilization segment M comprises amatrix stabilization block M1, which is arranged between the firstanchoring block A1 and the second anchoring block A2.

In alternative or additional exemplary embodiments, the anchoringsegment A comprises an anchoring block having a distribution ofrepeating units R1 and repeating units R2 within the anchoring block.Said distribution is not limited. The distribution may be an alternatingdistribution, a statistical distribution or any other distribution.

(Anchoring Segment A) (Non-Ionic Less Hydrophobic Repeating Unit R1)

The repeating unit R1 of the anchoring segment A is formed using anon-ionic less hydrophobic monomer MTh, which may be selected from thegroup of the group consisting of a methacrylate, an acrylate, and vinylmonomers.

In particular, the repeating unit R1 is a non-ionic repeating unit,meaning that the repeating unit R1 does not comprise an ionic moiety.

The repeating unit R1 comprises a (poly)alkylene oxide coupled to aterminal group via a direct bond, a —C—O—C— ether bond or a—C—O—(C═O)—N— urethane bond, wherein the terminal group is selected froman alkyl group, an aryl group and combinations thereof.

The alkyl group as herein provided, by itself or as part of anothergroup such as the alkylaryl and alkylene groups herein provided, refersto a fully saturated hydrocarbon of Formula C_(x)H_(2x+1) wherein x is anumber greater than or equal to 1. Generally, alkyl groups of thisinvention comprise from 1 to 20 carbon atoms. In the context of thepresent invention the term “alkyl” includes linear or branched alkyl andmay be substituted as indicated herein. In a particular embodiment theterminal group comprises a C₁-C₆ alkyl, wherein said C₁-C₆ alkylincludes all linear, or branched alkyl groups with between 1 and 6carbon atoms, and thus includes methyl, ethyl, n-propyl, i-propyl, butyland its isomers (e.g. n-butyl, i-butyl and t-butyl); pentyl and itsisomers, and hexyl and its isomers. In another embodiment and as part ofthe (poly)alkylene oxide group, the alkyl consists of a C₁₋₄ alkylwherein said C₁₋₄ alkyl includes all linear, or branched alkyl groupswith between 1 and 4 carbon atoms, and thus includes methyl, ethyl,n-propyl, i-propyl, butyl, and its isomers (e.g. n-butyl, i-butyl andt-butyl).

The aryl group as herein provided refers to a polyunsaturated, aromatichydrocarbyl group having a single ring (i.e. phenyl) or multiplearomatic rings fused together (e.g. naphthalene or anthracene) or linkedcovalently, typically containing 6 to 10 atoms; wherein at least onering is aromatic. Aryl is also intended to include the partiallyhydrogenated derivatives of the carbocyclic systems enumerated herein.Non-limiting examples of aryl comprise phenyl, biphenylyl, biphenylenyl,5- or 6-tetralinyl, 1-, 2-, 3-, 4-, 5-, 6-, 7-, or 8-azulenyl, 1- or2-naphthyl, 1-, 2-, or 3-indenyl, 1-, 2-, or 9-anthryl, 1-2-, 3-, 4-, or5-acenaphtylenyl, 3-, 4-, or 5-acenaphtenyl, 1-, 2-, 3-, 4-, or10-phenanthryl, 1- or 2-pentalenyl, 1,2-, 3-, or 4-fluorenyl, 4- or5-indanyl, 5-, 6-, 7-, or 8-tetrahydronaphthyl,1,2,3,4-tetrahydronaphthyl, 1,4-dihydronaphthyl,dibenzo[a,d]cylcoheptenyl, and 1-, 2-, 3-, 4-, or 5-pyrenyl.

In the context of the present invention the term “substituted” refers toa linear, aromatic or cyclic alkyl group optionally substituted with oneor more substituents (for example 1 to 4 substituents, for example 1, 2,3, or 4 substituents or 1 to 2 substituents) at any available point ofattachment. Non-limiting examples of such substituents include halo,hydroxyl, carbonyl, nitro, amino, oxime, imino, azido, hydrazino, cyano,aryl, heteroaryl, cycloalkyl, acyl, alkylamino, alkoxy, thiol,alkylthio, carboxylic acid, acylamino, alkyl esters, carbamate,thioamido, urea, sulfonamido and the like.

Preferably, the terminal group is an alkyl group; more preferably aC₁-C₆ alkyl optionally substituted with a one or more substituentsselected from hydroxyl and aryl. In specific examples, monomer Mn₁ isselected from the group of alkoxyether acrylate monomers, alkoxyethermethacrylate monomers, and urethane acrylate monomers.

In specific examples, the repeating unit R1 comprises a polyalkyleneoxide group, the polyalkylene oxide group comprises glycol unitsindependently selected from ethylene glycol and propylene glycol.

Exemplary embodiments of the repeating unit R1 are shown in Formula I:

wherein x=0-30, y=0-15, wherein x+y is at least 1, z=0-1, A is an alkyl,an aryl or an alkylaryl group; B=—H or —CH₃, and wherein A is connectedto the repeating unit either through a direct bond or through a urethanegroup. Preferably, A is an alkyl.

The repeating unit R1 according to Formula I is formed form a vinylmonomer, an acrylate monomer or methacrylate monomer, having a terminalether group, having A is an alkyl, an aryl or an alkylaryl group, andincludes one or more ethylene glycol groups and/or one or more propyleneglycol groups.

The optional terminal ether group may be formed by converting a hydroxylend group of a terminal glycol group.

Preferably, R1 being less hydrophobic than R2 is based on comparing aHansen Solubility Parameter value δ(polar+hydrogen)_(R1) of R1 beinghigher than a Hansen Solubility Parameter value δ(polar+hydrogen)_(R2)of R2. The Hansen Solubility Parameters according to the invention arecalculated according to Y-MB methodology using HSPiP software version5.2.03.

According to the Hansen Solubility Parameters theory, this sum isdefined as the square root of the sum of the square of the polar bondingvalue and the square of the hydrogen bonding value of the repeatingunit: δ(polar+hydrogen)=√[δ(polar)²+δ(hydrogen)²].

In specific examples, the repeating unit R1 has a Hansen SolubilityParameter value δ(polar+hydrogen)_(R1), whereinδ(polar+hydrogen)_(R1)>8.0 cal^(1/2) cm^(3/2), wherein the HansenSolubility Parameter value δ(polar+hydrogen) is defined as√[δ(polar)²+δ(hydrogen)²].

In an exemplary embodiment, the polar bonding value of R1:δ(polar)_(R1)>5.0 cal^(1/2) cm^(3/2).

The repeating unit R1 is preferably formed from an acrylate or amethacrylate.

In specific examples, the non-ionic less hydrophobic monomer Mn₁ is atleast one of tri(ethylene glycol) methyl ether acrylate,2-(2ethoxyethoxy)ethyl acrylate (EOEOEA), ethylene glycol methyl ethermethacrylate, 2-ethoxyethyl methacrylate, di(ethylene glycol) methylether methacrylate, tri(ethylene glycol) methyl ether methacrylate,phenoxyethyl methacrylate, ethylene glycol methyl ether acrylate,2-ethoxyethyl acrylate, di(ethylene glycol) methyl ether acrylate,2-[[(butylamino)carbonyl]oxy]ethyl acrylate, and mixtures thereof.

(Hydrophobic Repeating Unit R2)

The repeating unit R2 of the anchoring segment A is formed using ahydrophobic monomer Mn₂, which may be selected from the group consistingof a methacrylate, an acrylate, and vinyl monomers.

In an exemplary embodiment, the repeating unit R2 has a HansenSolubility Parameter value δ(polar+hydrogen)_(R2), whereinδ(polar+hydrogen)_(R2)<8.0 cal^(1/2) cm^(3/2), preferably <7.2 cal^(1/2)cm^(3/2), wherein the Hansen Solubility Parameter valueδ(polar+hydrogen) is defined as √[δ(polar)²+δ(hydrogen)²].

The repeating unit R2 is more hydrophobic than repeating unit R1, whichcorresponds to a lower sum of the polar bonding value and the hydrogenbonding value of R2.

In an exemplary embodiment, the polar bonding value of R2:δ(polar)_(R2)<5.0 cal^(1/2) cm^(3/2), preferably <4.4 cal^(1/2)cm^(3/2). The repeating unit R2 is more hydrophobic than repeating unitR1, which corresponds to a lower polar bonding value of R2.

In specific examples, the hydrophobic monomer Mn₂ is at least one ofbenzyl methacrylate, butyl methacrylate, methyl methacrylate, ethylmethacrylate, propyl methacrylate, hexyl methacrylate, 2-ethylhexylmethacrylate, octyl methacrylate, lauryl methacrylate, stearylmethacrylate, p-tolyl methacrylate, sorbyl methacrylate, benzylacrylate, butyl acrylate, methyl acrylate, ethyl acrylate, propylacrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, laurylacrylate, stearyl acrylate, p-tolyl acrylate, sorbyl acrylate, andmixtures thereof.

(Combination of Repeating Unit R1 and Repeating Unit R2 in the AnchoringSegment A)

In an exemplary embodiment, the repeating unit R2 of the anchoringsegment A is formed using a hydrophobic monomer Mn₂, which is selectedfrom the group consisting of a methacrylate, an acrylate, and vinylmonomers, and the repeating unit R1 of the anchoring segment A is formedusing a non-ionic less hydrophobic monomer Mn₁, which is selected fromthe group of the group consisting of a methacrylate, an acrylate, andvinyl monomers.

In particular, the repeating units R1, R2 of the anchoring segment A donot have an ionic group. Preferably, the repeating units R1, R2 are bothhydrophobic in nature compared to the aqueous matrix. As such, theanchoring segment A does substantially not dissolve in the aqueouscarrier phase.

In an exemplary embodiment, the anchoring segment A has a number ofrepeating units n and wherein the sum of the repeating units R1 and therepeating units R2 is at least 50 number-% of the total number ofrepeating units n, preferably at least 80 number-% of the total numberof repeating units n.

In an exemplary embodiment, the ratio between the number of repeatingunits R1 (n1) and the number of repeating units R2 (n2) is between 0.05and 20, preferably between 0.1 and 10.

(Matrix Stabilisation Segment M)

A repeating unit of the matrix stabilization segment M may be formedusing a monomer Mn₃. In case two different monomers Mn₃ are used to formthe matrix stabilization segment M, the matrix stabilization segment Mhas a first repeating unit and a second repeating unit, each formed by arespective, different, monomer Mn₃. In that case, the number of firstrepeating units and the number of second repeating units of segment Mtogether sum up to the total number n of repeating units of segment M,i.e. the matrix stabilization part of the first block.

In particular, the at least one ionic hydrophilic repeating unit R3 ofthe matrix stabilization segment M comprises an ionic moiety.

Additionally, the matrix stabilization segment M may comprise othernon-ionic repeating units additionally to the ionic hydrophilicrepeating units. In an exemplary embodiment, the matrix stabilizationsegment M may comprise ionic hydrophilic repeating units and non-ionicmatrix stabilizing repeating units contain (poly)glycol functionalities.The ionic hydrophilic repeating units and non-ionic repeating units ofthe matrix stabilization segment M cooperatively contribute to the watersolubility of the polymer.

(Ionic Repeating Unit R3)

In specific examples, the matrix stabilization segment M is formed usingat least one monomer Mn₃ for obtaining an ionic hydrophilic repeatingunit R3, respectively. The ionic hydrophilic repeating unit R3preferably containing a neutralized acid group, neutralized basic group,such as protonated amino group, or other ionic functionalties such as aquaternary ammonium group.

The ionic hydrophilic repeating unit R3 provides solubility of thematrix stabilization segment M in the aqueous carrier phase.

In specific examples, the monomer Mn₃ is selected from the groupconsisting of methacrylic acid, acrylic acid, maleic acid, maleic acidmonoester, itaconic acid, itaconic acid monoester, crotonic acid,crotonic acid monoester, N,N-dimethylaminoethyl methacrylate,N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate,N,N-diethylaminoethyl acrylate, t-butylaminoethyl methacrylate,t-butylaminoethyl acrylate, and mixtures thereof.

In case the matrix stabilizing segment contains hydrophilic repeatingunits with acid functionality, a considerable part of the acid groupsneed to be neutralized to provide solubility and dispersion stability,preferably all acids are neutralized by setting the pH level to 7.5 andmost preferably the pH is set to 8.5 or above. In case the matrixstabilizing segment contains hydrophilic repeating units with basicgroup functionality a considerable part of the basic groups areneturalized to provide solubility and dispersion stability, preferablyall basic groups are neutralized by setting the pH level to 6.5 and mostpreferably the pH is set to 5.5 or below.

The choice of the neutralizing agent and thus the corresponding usedsalt counter ion of the repeating unit R3 determines the modified,repeating unit R3 in such way that this has to be considered as adifferent chemical structure.

Possible neutralization agents for acid groups are tertiary amines suchas trimethylamine and triethylamine, triethanolamine, ammonia,2-dimethylamino ethanol, 2 amino-2 methyl 1 propanol, 2(2amino-ethylamino) ethanol, 2 amino-2methyl 1 propanol, sodiumhydroxide, potassium hydroxide, and the like.

Possible neutralization agents for basic groups include inorganic acidssuch as hydrochloric acid and sulfuric acid; and organic acids such asacetic acid, citric acid, maleic acid, propionic acid, lactic acid,succinic acid and glycolic acid.

The present invention is not limited to those exemplified ones.

The selection of the neutralizing agent and corresponding salt counterion of the repeating unit R3 may have an effect on pigment dispersionstability; including an effect on a pigment particle grindingcharacteristic and speed of the pigment dispersion and/or including aneffect on a pigment dispersion stability characteristic when exposed toextreme conditions. The selection of the neutralizing agent, pH valueand corresponding salt counter ion can influence the behaviour of thefinal ink, e.g. the drying speed, open time, first drop reliability andthe jetting stability.

(Pigment)

For water based inks the pigment surface has in general a morehydrophobic nature that the bulk liquid. Therefore anchoring monomerslike alkyl acrylates and aryl acrylates, like benzyl acrylates, can beused. However some pigments have been found to have additional pigmentsurfaces being less hydrophobic and these pigments have been found moredifficult to realize a good milling performance with one anchoringrepeating unit in the block dispersant only.

The differences or variations in pigment surfaces may be shown bychemical analysis or by the synthesis procedure of the pigment or canexperimentally be demonstrated by HSPIP/Hansen Solubility methodology.In this methodology the solubility of the substance may be evaluated indifferent solvents and as a result the solubility/compatibility may beexpressed as a hydrogen force, a dipole force and Vanderwaals/dispersiveforce. Pigments which may have clearly differing pigment surfaces area.o. PR122, PBk7, PB15.3, PY74 and PY155.

The anchoring segment A of the block copolymer dispersant D thuscontains different repeating units that may be selected for differentanchoring sites on the pigment surface. For example, in case of acrystalline structure of the pigment, surfaces with different chemicalnature may exist and may need different anchoring chemistry to achievinghigher pigment dispersion stability.

In exemplary embodiments, the pigment P is a color pigment selected foradjusting a color of the ink. In exemplary embodiments, the pigment P isan organic pigment, optionally comprising a metal atom complexed with anorganic component of the organic pigment.

In exemplary embodiments, the pigment P is a inorganic pigmentoptionally comprising a metal oxide.

In a particular exemplary embodiment, the magenta pigment is aquinacridone pigment selected from Pigment Red 122, Pigment Violet 19and Pigment Red 202, or the magenta pigment is Pigment Red 57:1, and/orwherein the cyan pigment is Pigment Blue 15:3, Pigment blue 15.4,pigment blue 15.6 and/or wherein the yellow pigment is selected fromPigment Yellow 155 and Pigment Yellow 74, and pigment yellow 180 and/orwherein the black pigment is a carbon black, preferably Pigment Black 7.

(Aqueous Pigment Dispersion)

Preferably, the amount of water in the aqueous carrier is at least 50wt.-%, preferably at least 80 wt.-%, more preferably at least 95 wt.-%,of the total weight of the aqueous carrier.

In specific examples, the aqueous carrier contains a total amount ofwater soluble organic solvent, which is less than 20 wt %, preferablyless than 10 wt %, in particular preferably less than 5 wt %, of thetotal weight of the aqueous carrier. Preferably, the aqueous carriercontains substantially no water soluble organic solvent.

The relatively high amount of water in the aqueous carrier, and/orrelatively low amount of water soluble organic solvent or no watersoluble organic solvent, enhances a versatile easy use of manufacturinginkjet inks derived from the Aqueous Pigment Dispersion.

In an exemplary embodiment, the amount of pigment P in the pigmentdispersion is in the range of 10-60 wt-% based on weight of the pigmentdispersion. The pigment dispersion may be a concentrated dispersion ofpigment P compared to an inkjet ink derived from the pigment dispersion.In general, an amount of coloured pigment P in the inkjet ink may be inthe range of 0.5-10 wt-% based on weight of the inkjet ink.

In case of an inorganic, preferably white, pigment the amount of pigmentP in the pigment dispersion may be in the range of 40-80 wt % based onweight of the pigment dispersion and in the final inkjet ink from 10-50wt-% based on weight of the inkjet ink.

In an exemplary embodiment, the weight ratio between the pigment P andthe block copolymer dispersant D is between 0.1 and 10.0, preferablybetween 0.4 and 5.

(Method for Preparing Aqueous Pigment Dispersion)

Preferably, the Aqueous Pigment Dispersion is prepared without the useof water soluble organic solvents or other organic solvents.

The pigment dispersion is prepared by mixing the raw materials in theappropriate ratios. The pigment concentration is typically between 10and 60 wt-% and the weight ratio pigment/block dispersing agent istypically 0.1 to 10. Other ingredients beside the pigment, dispersingagent and water can be added to improve the pigment dispersion processlike wetting agents (typically Mw<1000 g/mol) and the like.

Preferably, no or only a limited amount of water soluble co-solvents(like alkyl ethers or glycols) are used for preparing the AqueousPigment Dispersion.

It is beneficial to perform a very good mixing of the raw materials byknown methods in the art like cowls mixers, dissolvers, to obtain a verygood premix before starting the final dispersion step.

No particular limitation is imposed on the dispersion method. Examplesof dispersion methods are paint shakers, horizontal and vertical beadmills and high pressure homogenizers. In order to assure a very goodanchoring of the dispersing agent on the pigment surface and or a verygood electro steric stabilization it can be beneficial to mill atelevated temperature (40 to 80° C.) or to perform a heat treatment at 40to 80° C. after the milling step for a certain time. This heat treatmentcan be carried out static or dynamic (i.e. some kind ofagitation/stirring of the dispersion during the heat treatment).

After milling is completed, the milling media is separated from themilled particulate using conventional separation techniques, such as byfiltration, sieving through a mesh screen, and the like. Often the sieveis built into the mill, e.g. for a bead mill.

Preferably the block copolymer dispersant is dissolved in an aqueousmedium before making the pre-dispersion. The dissolved polymer isachieved by mixing the dried block copolymer with water, and if requiredadditional neutralization agent, for at least 2 h at room temperature.Stirring and/or increasing the temperature up to 60° C. may be used toaccelerate the dissolution process.

(Aqueous Pigmented Inkjet Ink)

Any amount of additional water and water soluble organic co-solvents maybe added to the pigment dispersion to form inkjets according to theinvention. Any other suitable additives, such as surfactants, binders,dispersing aids, thickeners, pH-adjusting agents, etc., may be added tothe pigment dispersion to form inkjet inks according to the invention.

In an exemplary embodiment, the ink is an aqueous ink having an aqueouscarrier. The aqueous carrier is liquid at room temperature. The aqueouscarrier comprises water and optionally water soluble organic co-solventor co-solvents for carrying or suspending the pigment P including theblock copolymer dispersants D.

In an exemplary embodiment, the amount of pigment in the ink is at least0.5 wt-%, preferably at least 1 wt-%, relative to the total weight ofthe ink, wherein preferably the ink has a viscosity of at most 30 mPa·sat 25° C.

In exemplary embodiments, the viscosity of the inkjet inks is between 4and 30 mPa·s at 25° C., preferably between 4 and 20 mPa·s at 25° C.

In exemplary embodiments, the static surface tension of the inkjet inksis between 17 and 35 mN/m.

In particular, the ink may contain at least one binder resin forimproving at least one of adhesion to a substrate, drying, water orscratch resistance of the ink on a substrate. Said binder resin may be awater soluble resin or may be provided as resin microparticles. Theresin microparticles are dispersed in the inkjet ink as emulsions orlattices.

The inkjet ink containing binder may be used for enhanced adhesion ofthe pigment to the substrate while maintaining a high pigment stability.The pigment dispersion of the inkjet ink according to the invention hasbeen found to maintain the high stability when used in combination withsaid at least one binder resin.

(Water Soluble Organic Solvent)

In an exemplary embodiment, the water soluble organic solvent comprisesat least one of a polyol compound, an a glycol ether compound, such as a(poly)ethyleneglycol ether or (poly)propyleneglycol ether compound. Apolyol compound in the context of this application is the same as apolyhydric alcohol, i.e. having at least two alcohol groups like forexample glycerol and propyleneglycol. In a particular exemplaryembodiment, the water soluble glycol ether compound is a glycolmonobutyl ether.

A water soluble organic solvent may be selected being a penetrant forimproving permeability (wettability) of the ink into the substrate. Apenetrant supports adjusting a dot diameter on the substrate and/orimproves adhesion of the pigment to the substrate. Particular suitablepenetrants have surface tension active properties thereby lowering thesurface tension of the ink.

Exemplary penetrants include alkanediols and glycol ethers. It has beenfound by the inventors that water soluble organic solvents havingpenetrant properties tend to compete with dispersants, which stabilizethe pigment.

An exemplary penetrant is a glycol monobutyl ether, such as diethyleneglycol monobutyl ether or ethylene glycol monobutyl ether. It should benoted that some penetrants like diethylene glycol monobutyl ether,ethylene glycol monobutyl ether, dipropyleneglycol monomethyl ether,ethylene glycol isopropyl ether, 1,2-hexanediol have surface tensionactive properties thereby lowering the surface tension of the ink.

In an exemplary embodiment, the weight-concentration of the at least onewater soluble organic solvent, in the ink is in the range of 5 wt-% -40wt-%, preferably in the range of 5 wt-% -30 wt-%, based on the totalweight of the ink.

In a particular embodiment, the weight-concentration of the at least onepenetrant in the ink is in the range of 1 wt-% -15 wt-%, preferably inthe range of 2 wt-% -10 wt-%, based on the total weight of the ink.

(Aqueous Pigmented Inkjet Ink Set)

In specific examples, the inkjet inks of the ink set comprise a cyan inkcomprising a cyan pigment, a magenta ink comprising a magenta pigment, ayellow ink comprising a yellow pigment and a black ink comprising ablack pigment. The ink set may include any other colored pigmented inkand/or non-colored pigmented ink. The ink set may further include one ormore non-pigmented inks.

(Inkjet Printing Process)

In an exemplary embodiment, the inkjet printing process comprisingjetting droplets of each inkjet ink on the substrate to form a colorimage on the substrate.

In a particular exemplary embodiment, the droplets are jetted by usingan inkjet printhead.

In an exemplary embodiment, the inkjet process comprises forming theimage on a finished corrugated board, a corrugated liner, labelsubstrate like paper and filmic labels or flexible packaging substratein a single pass at speeds of at least 30 m/min, preferably at least 50m/min.

DETAILED DESCRIPTION

As used herein, the term “dispersion” means a two-phase system whereinone phase consists of finely divided particles (often in a colloidalsize range) distributed throughout a bulk substance, the particles beingthe dispersed or internal phase and the bulk substance being thecontinuous or external phase.

As used herein, the term “dispersant” means a surface active agent addedto a suspending medium to promote uniform and maximum separation ofextremely fine solid particles. For pigments, the dispersants can bepolymeric dispersants, and the dispersion comprising the dispersants andpigments is usually prepared using dispersing equipment.

As used herein, the term “aqueous” refers to water or a mixture of waterand at least one water soluble, or partially water soluble, organicsolvent (co-solvent). As used herein, the term “water based ink” has thesame meaning as the term “aqueous ink”.

As used herein, the term “substantially” means being of considerabledegree, almost all.

As used herein, the term “ink set” means a combination of inkjet inksused as a kit of parts for printing an image on a substrate by applyingthe inkjet inks on the substrate according to the present invention. Inparticular, the ink set is a combination of inkjet inks which may beused together in the same printing process to form a color image on thesubstrate.

The materials, methods, and examples herein are illustrative, and arenot intended to be limiting. The term “urethane” as used herein, must beunderstood to also include isomers of urethane, such asC—O—(C═O)—N<->C—O—(C—OH)═N isomers.

Aqueous Inks

The use of a colorant in inks is the most essential form of a waterbased ink. However in order to prevent drying of the ink at the nozzles,aqueous inks used in inkjet printing methods typically also contain awater soluble organic solvent having a high boiling point and favorablesolubility in water. This type of solvent may also be regarded as ahumectant in the aqueous ink.

Aqueous inks used in inkjet printing methods may typically also containa water soluble organic solvent being a penetrant for improvingpermeability (wettability) of the ink into the substrate. A penetrantsupports adjusting a dot diameter on the substrate and/or improvesadhesion of the pigment to the substrate. Particular suitable penetrantshave surface tension active properties thereby lowering the surfacetension of the ink. Further, to enable a minimal amount of wetting andspreading of water based inks in the printhead, on the substrate, etc.the aqueous inks used in inkjet printing methods typically also containone or more surfactants.

Finally, the aqueous ink composition may also contain various types ofadditives such as anti-foaming agents, thickeners, binders andpreservatives as required. Adding these types of additives to theaqueous ink composition enables the composition to be used morefavorably as an inkjet ink.

Pigment

A pigment is preferably used from the viewpoints of offering excellentwater resistance, light resistance, weather resistance and gasresistance or the like. Examples of pigments that may be used in thepresent invention include conventional organic pigments and inorganicpigments.

The pigment may be chosen from those disclosed by HERBST, W., et al.Industrial Organic Pigments, Production, Properties, Applications. 2ndedition. vch, 1997.

The pigment particles in the pigmented inkjet ink should be sufficientlysmall to permit free flow of the ink through the inkjet printing device,especially at the ejecting nozzles. It is also desirable to use smallparticles for maximum color strength and to slow down sedimentation.

The average particle size of the pigment in the pigmented inkjet inkshould be between 5 nm and 1 μm, particularly preferably between 5 nmand 500 nm and most preferably between 30 nm and 300 nm. Larger pigmentparticle sizes may be used as long as the objectives of the presentinvention are achieved.

The pigment is used in the pigmented ink jet ink in an amount of 0.1 to30 wt-%, preferably 1 to 10 wt-% based on the total weight of thepigmented inkjet ink.

Examples of cyan pigments that can be used in the present inventioninclude C.I. Pigment Blue 1, 2, 3, 15:3, 15:4, 15:6, 16 and 22, and C.I.Vat Blue 4 and 6. These cyan pigments may be used individually, or acombination of two or more pigments may be used.

Examples of magenta pigments that can be used in the present inventioninclude C.I. Pigment Red 5, 7, 12, 22, 23, 31, 48 (Ca), 48 (Mn), 49, 52,53, 57 (Ca), 57:1, 112 and 122; Quinacridone solid solutions 146, 147,150, 185, 238, 242, 254, 255, 266 and 269, and C.I. Pigment Violet 19,23, 29, 30, 37, 40, 43 and 50. Quinacridone mixed-crystal pigments canalso be used.

Examples of yellow pigments that can be used in the present inventioninclude C.I. Pigment Yellow 10, 11, 12, 13, 14, 17, 20, 24, 74, 83, 86,93, 94, 95, 109, 110, 117, 120, 125, 128, 137, 138, 139, 147, 148, 150,151, 154, 166, 168, 180, 185 and 213.

Other organic pigments can be used to enhance the color gamut like C.I.Pigment Green 36, and 7, Pigment Violet 23Pigment Orange 34 and 64.

Examples of black pigments that can be used in the present inventioninclude organic pigments such as aniline black, Lumogen black andazomethine black, and inorganic pigments such as carbon black and ironoxide. Further, a plurality of color pigments such as the aforementionedyellow pigments, magenta pigments and cyan pigments may be mixedtogether and used as a black pigment.

There are no particular limitations on the inorganic pigments that maybe used in the present invention. Examples of inorganic pigments mayalso include different metal oxides.

Additionally, the inorganic pigment can include a white pigment such astitanium dioxide (anatase, brookite and rutile) which is for examplecommercially available from KRONOS (e.g. grade 2044, 2047) or as metaloxide coated titanium dioxides (e.g. R700 E.I. DuPont de Nemours), orother inorganic pigments such as zinc oxide and iron oxide.

Examples of carbon black pigments that can be used in the presentinvention include carbon blacks produced using the furnace method or thechannel method.

Examples of commercial products are listed below, and any of theseproducts can be used favorably.

Specific examples of carbon black include No. 33, 40, 45, 52, 900,2200B, 2300, MA7, MA8 and MCF88 (all manufactured by Mitsubishi ChemicalCorporation), RAVEN 1255 (manufactured by Columbian Chemicals Co.,Inc.), REGAL 330R, 400R and 660R, and MOGUL L (all manufactured by CabotCorporation), and Nipex 1601Q, Nipex 1701Q, Nipex 75, Printex 85,Printex 95, Printex 90, Printex 35 and Printex U (all manufactured byOrion Engineered Carbons LLC).

In this embodiment of the present invention, the pigment is not limitedto the pigments described above, and other special colors such as orangepigments and green pigments can also be used.

Further, a plurality of pigments may be combined. Moreover, in anotherembodiment, the aqueous ink composition of this embodiment of thepresent invention may be combined with a clear ink containing no pigmentand used as an ink set.

Any other pigment and/or dye can be used that is useful in modifying thecolor of the ink.

Surfactant

The inkjet ink according to the present invention may contain at leastone surfactant. The surfactant(s) can be anionic, cationic, non-ionic,or zwitter-ionic and are usually added in a total quantity less than 6wt-% based on the total weight of the pigmented inkjet ink andparticularly in a total less than 4 wt-% based on the total weight ofthe pigmented inkjet ink.

Suitable surfactants for the inkjet ink according to the presentinvention include silicon-based, acrylic-based and fluorine-basedsurfactants, fatty acid salts, ester salts of a higher alcohol,alkylbenzene sulphonate salts, sulphosuccinate ester salts and phosphateester salts of a higher alcohol, ethylene oxide adducts of a higheralcohol, ethylene oxide adducts of an alkylphenol, ethylene oxideadducts of a polyhydric alcohol fatty acid ester, and acetylene glycoland ethylene oxide adducts thereof. Commercial examples include Byk-348,Byk-347, Byk-3450, Dynwet 800 (Byk Chemie Gmbh); Surfynol 104, Surfynol465, Metolat 364, Dynol 800, Dynol 960, (Evonik Industries), KF-640,KF-642 (Shin-Etsu); ID-40, ID-70 (Sanyo Chemical industries), OlfineE1004, Olfine E1010, Olfine EXP4300, Silface SAG503 all of NisshinChemical; etc and combinations thereof.

Water Soluble Organic Solvent

The type of water soluble, organic, solvent is not particularly limitedinsofar as the effects of the present invention can be obtained. It ispreferable that the organic solvent is water soluble from the viewpointof increasing the compatibility with respect to water. Examples of thewater soluble organic solvent include alcohols, polyhydric alcohols,amines, amides, glycol ethers, 1,2-alkanediols and the like. Only onetype of the organic solvent may be used, or two or more types thereofmay be used.

Examples of polyhydric alcohols described above include ethylene glycol,diethylene glycol, triethylene glycol, tetraethylene glycol,polyethylene glycol having the number of ethylene oxide groups ofgreater than or equal to 5, propylene glycol, dipropylene glycol,tripropylene glycol, polypropylene glycol having the number of propyleneoxide groups of greater than or equal to 4, butylene glycol, hexanediol,pentanediol, glycerin, hexanetriol, thiodiglycol, and the like.

Examples of amines described above include ethanol amine, diethanolamine, triethanol amine, N-methyl diethanol amine, N-ethyl diethanolamine, morpholine, N-ethyl morpholine, ethylene diamine, diethylenediamine, triethylene tetramine, tetraethylene pentamine, polyethyleneimine, pentamethyl diethylene triamine, tetramethyl propylene diamine,and the like.

Examples of amides described above include formamide, N,N-dimethylformamide, N,N-dimethyl acetamide, pyrolidone, urea and the like.

Examples of glycol ethers described above include ethylene glycolmonoethyl ether, ethylene glycol monobutyl ether, diethylene glycolmonoethyl ether, diethylene glycol monobutyl ether, triethylene glycolmonobutyl ether, propylene glycol monopropyl ether, dipropylene glycolmonomethyl ether, tripropylene glycol monomethyl ether, and the like.

Examples of 1,2-alkanediols include 1,2-propanediol 1,2-butanediol,1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and the like.

Among them, in a case where the water soluble organic solvent ispolyhydric alcohols, blur at the time of performing printing at a highvelocity can be preferably suppressed. Preferred examples of polyhydricalcohols include ethylene glyckol, diethylene glycol, triethyleneglycol, tetraethylene glycol, propylene glycol, dipropylene glycol,tripropylene glycol, and the like.

Water soluble organic solvents may be selected being a penetrant forimproving permeability (wettability) of the ink into the substrate. Apenetrant supports adjusting a dot diameter on the substrate and/orimproves adhesion of the pigment to the substrate. Particular suitablepenetrants include alkanediols and glycol ethers.

Binder Resin

In one embodiment, the aqueous ink composition of the present inventionpreferably also contains a binder resin (functional polymer). Knownbinder resins for aqueous ink compositions include water soluble resinsand resin microparticles (emulsions/latexes). Examples of types ofresins that can be used as the resin microparticles includeacrylic-based, styrene/acrylic-based, urethane-based,styrene/butadiene-based, vinyl chloride-based, vinylacetate-based(possibly partially or fully hydrolysed), polyester-based, andpolyolefin-based resins.

These additional binder resins may aid in achieving a stable jettingprocess, adhesion of the ink to the substrate, chemical and/ormechanical resistance of the final ink layer, or improve image quality.

Biocides

Suitable biocides for the pigmented inkjet ink of the present inventioninclude sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodiumpyridinethion-1-oxide, ethyl p-hydroxybenzoate,2-methyl-1,2-thiazol-3-one and 1,2-benzisothiazolin-3-one and saltsthereof. A biocide is preferably added in an amount of 0.001 to 3 wt-%,more preferably 0.01 to 1.00 wt-%, each based on the total weight of thepigmented inkjet ink.

Other Components

In the inkjet printing ink, various known additives, for example,polysaccharides, a viscosity adjuster, a film forming agent, a pHadjuster and the like can be suitably selected and used in addition tothe components described above, as necessary, according to the object ofimproving all performances.

Preparation of a Pigmented Inkjet Ink

The pigmented inkjet ink according to the present invention may beprepared by first preparing the pigment dispersion and afterwards dilutethe pigment dispersion to the desired pigment concentration and addingall the other ink components, such as adding the water soluble organicsolvents needed.

It is desirable to make the color ink in the form of a concentratedAqueous Pigment Dispersion according to the invention, which issubsequently diluted to the appropriate concentration for use in theinkjet printing system. This technique permits preparation of a greaterquantity of pigmented ink from the equipment. By dilution, the ink isadjusted to the desired viscosity, color, hue, saturation density, andprint area coverage for the particular application.

The inkjet inks are prepared by mixing the components with thedispersion using regular mixing devices. A method for the stirring andmixing is not particularly restricted and may be appropriately selectedaccording to necessity, using a homogenizer, a paint shaker, anultrasonic disperser, a stirrer using ordinary stirring blades, amagnetic stirrer, and a high-speed disperser, for example. The ink isfinally filtered before use. With drop sizes less than 20 pl in manycases, and printhead nozzles smaller than 30 microns, a filtration stepin the range of 1 to 5μm is implemented. It is vital to ensure noparticulates reach the nozzles, as a single failure can lead to thereplacement of an entire printhead at significant cost.

For pigmented inks, multiple-stage filtration is typically used aftercreation of the dispersion, and again after addition of additives anddilution. Here the main objectives are removal of any oversized oragglomerated pigments from the dispersion, as well as any oversizedparticles and contaminants from other processes.

The available filter technologies have different applications,advantages and disadvantages. Examples of filter are: membrane, depthand hybrid filter types. Common suppliers of filters for inkjet inks arePall, Porvair, Membrane Solutions.

In a preferred embodiment, no crosslinking or encapsulation is neededafter milling. The stable pigment dispersion according to the inventioncan be obtained without the need of crosslinking and other additionalsteps, e.g. filtration step to remove unreacted material, etc. areobsolete. This results in a simpler synthesis process and iseconomically more interesting since less energy and resources need to bespent to obtain a stable pigment dispersion.

Optionally, adding a crosslinking and or encapsulation step results inan even more stable dispersion but this process is more complex and moresensitive to unreacted crosslinking agent and/or crosslinked freedispersing agent. This could potential lead to less performant pigmentdispersions and corresponding inks when no extra removal step like forexample ultrafiltration is used.

Experimental Manufacturing Processes Block Copolymers Synthesis

Block copolymers can be prepared using an array of different, so-calledliving, polymerization methods. The basis of the method is invariable ofthe synthetic method used:

-   -   An instantaneous initiation, which ensures simultaneously        growing of all the polymer chains at a specific propagation        speed.    -   Living polymerization is ensured by adding very small        concentrations of active (propagating) chains into the solution        at a given time, in order to avoid termination or recombination        of radicals.    -   Continued propagation is strictly controlled, thereby obtaining        a small polydispersity of the polymer and thus a well-defined        polymer composition.

Further polymerization can be achieved in a number of ways but anionicpolymerization and group transfer polymerization (e.g. Atom-TransferRadical-Polymerization [ATRP], NMP, . . . ) are the two most commonsynthetic methods. These methods have such specific requirements (nooxygen, no water, . . . ) which make them impractical and expensive whenproducing large (industrial-sized) volumes of polymers. Two examplesthereof are the use of alkyl lithium components at very lowtemperatures, or naphthanelides to initiate polymerization.

In an exemplary embodiment the block copolymer is prepared by ATRP asdescribed in Controlled living radical polymerization. by Wang andMatyjaszewski (macromolecules 1995, 28 7901-7910).

Synthesis Examples

The below procedure describes a potential synthesis method to producethe block dispersing agent, which is characterized asAA₁₅-(BnA₃₀/EOEOEA₁₀) having 15 monomers AA for its matrix stabilizationblock length and 30 monomers benzyl acrylate (BnA)+10 monomers2-(2-ethoxyethoxy)ethyl acrylate (EOEOEA) for its anchoring blocklength. It is a block copolymer dispersant comprised of two blocks,wherein the matrix stabilization segment is formed by reacting themonomer AA and has a length of about 15 repeating units and theanchoring segment is formed by reacting the monomer BnA together withEOEOEA and has a length of about 40 repeating units in total. Otherblock dispersant architectures can be produced by someone skilled in theart in the same manner by adjusting the amounts and kinds of startingmaterials and reaction times and the sequence of preparation of theblock dispersing agent can be exchanged i.e. first making the BnA/EOEOEAblock and afterwards the AA block. “Parts” in the description is basedon mass unless noted otherwise.

A 500-milliliter triple neck flask equipped with a thermometer, abackflow condenser, and a nitrogen balloon was charged with 1.43 partsof Cu(I)Br, 38.5 parts of tert-butyl acrylate, 41.2 parts of anisole, aninternal standard and 1.73 parts ofN,N,N′,N″,N″-Pentamethyldiethylenetriamine (PMDETA). The mixture wasdegassed under vacuum and back-filled with nitrogen three times andheated to 80° C. Subsequently, 3.34 parts of methyl 2-bromopropionate(MBP) were added to initiate the polymerization reaction, which wasconducted for 1 h.

In a separate flask, 97.3 parts of benzyl acrylate, 37.6 parts of2-(2-ethoxyethoxy)ethyl acrylate, 59.6 parts of anisole and 1.73 partsof PMDETA were mixed and degassed under vacuum and back-filled withnitrogen three times. This solution was added to the tert-butyl acrylatepolymer solution together with 0.64 parts of Cu(0). The polymerizationwas stopped after 6 h (Mn=8807 and Mw/Mn=1.29) by exposing the catalystto air. The copper catalyst was removed by column chromatography, afterwhich the excess solvent was removed by evaporation.

Subsequently, the tert-butyl acrylate groups of the block copolymer werehydrolyzed. The purified block copolymer was dissolved in 2 volume partsdioxane under reflux, after which 0.5 equivalents of sulfuric acid,compared to the amount of tert-butyl acrylate repeating units of thepolymer, were added to the solution. After 2 hours, an equimolar amountof base was added to stop the reaction. The reaction solution wasfiltrated over Celite® to remove the formed salts. Dioxane was removedby rotary evaporation, to yield the acrylic acid/benzylacrylate/2-(2-ethoxyethoxy)ethyl acrylate block copolymer

The current synthesis method describes the “common” reactor-basedsynthesis. Alternatively, a Flow chemistry process can be employed tosynthesize the mentioned block dispersing agents. The inventors refer to“Flow Chemistry: Integrated Approaches for Practical Applications”,Santiago V Luis, Eduardo Garcia-Verdugo (Ed.), 2019, (ISBN:978-1-78801-498-4/978-1-78801-609-4). The block dispersant wassynthesized using a flow reactor using the same starting materials asthe “common reactor” except EBiB was used as an initiator, 365 nm UV LEDlight as a source of photons, the reaction was initiated by reduction ofCu(II)Br₂ to Cu(0) and the solvents used were acetonitrile:ethanol 1:1.The flow reactor was assembled with PFA tubing ( 1/16″ OD, 0.75 mm ID).The streams were respectively connected via inline check valves, T-pieceand a static mixer before entering the photoreactor to ensurehomogeneity. 16 LEDs (365 nm) were assembled on the octagonal reactor(in house built using 3D printer, with a PLA filament). The secondpolymer block can be added to the first block in a subsequent reactormodule. Finally, hydrolysation and filtration steps can be performedsimilar to the batch process described above or integrated in the flowreactor setup.

In order to make the dispersant compatible with the carrier, thehydrophilic monomer needs to be neutralized thereby ionizing thesalt-forming group of the block copolymer. As the neutralizing agent,there can be used an acid or a base depending upon the kinds of thesalt-forming group, e.g. basic such as DMAEMA or acidic such as(meth)acrylic acid. The neutralizing agent for basic monomers includes,for instance, inorganic acids such as hydrochloric acid and sulfuricacid; and organic acids such as acetic acid, propionic acid, lacticacid, succinic acid and glycolic acid. In addition, the neutralizingagent for acidic monomers includes, for instance, tertiary amines suchas trimethylamine and triethylamine, triethanolamine, ammonia,2-dimethylamino ethanol, 2 amino-2 methyl 1 propanol, 2(2amino-ethylamino) ethanol, 2 amino-2methyl 1 propanol, sodiumhydroxide, potassium hydroxide, and the like. The present invention isnot limited to those exemplified ones.

Note that the total dispersant weight mentioned in the examples belowincludes the mass of the neutralizing agent.

Water Solubility of Block Copolymer Dispersants

Example of solubilization is listed in Table 1. Test of water solubilityis carried out according to the test procedure described further below.

TABLE 1 weight % in water solubilized, Dissolution stable neutralizationconditions at 25° C. for polymer agent matrix time temperature 1 week(*) (BnA₃₀/EOEOEA₁₀)—Na₁₅ MEA distilled H2O 6 h 25° C. 25%

Dissolution was carried out in round flask using mechanical stirring.(*) stability is checked by decanting aqueous polymer solution andchecking for solid sedimentation.

Encapsulation

Optionally, crosslinking is performed right after the milling process bychemically coupling the dispersing agents together on the surface. Avery popular method to achieve this sees an epoxy compound (mostly di-or tri-epoxides) added to the dispersion in order to couple a certainportion of the (meth)acrylic acid monomers present in the dispersingagent backbone (preferably on the surface of the pigment particle). Ifnot all dispersant is adhered to the pigment surface then these freepolymers will disturb the crosslinking process e.g. by being built inbetween polymer particles and thus flocculating part of the dispersionand therefore have to be removed afterwards. These resultingencapsulated pigment particles will possess great stability because ofthe formation of a “net” or “capsule” of dispersing agent across thesurface of the particle, which cannot be disturbed by the addition ofco-solvents and surfactants.

Pigment Dispersion Production

A pigment dispersion having a composition according to Table 2 isprepared by milling 30 g of raw materials in a ball jar with a pigmentconcentration of 15%.

The ball jar milling is performed in PP bottles of 125 mL with adiameter of 45 mm. The bottles are filled with 200 g of 0.3 mm YTZceramic beads from Tosoh. The milling is done at a rotational speed of36 m/min for 7 days.

TABLE 2 Pigment dispersion composition weight weight (examples (examplescomponent 1-10) 11-12) Pigment 4.5 g 4.5 g Block dispersant 4.5 g 2.25 g(according table 4), neutralized with sodium hydroxide water 21 g 23.25g Total 30 g 30 g

Analytical Methods Particle Size Analysis

The particle size of pigments is determined on a Nicomp 3.80 particlesizer (Particle sizing systems, Santa Barbara California USA). Thedispersion is diluted to 10 to 100 ppm to reach optimal measurementperformance (i.e. the dispersion is diluted 10*10⁶ times to 100*10⁶times). The diluted samples are measured at 23° C. with a HeNe laser andthe dv50 is obtained from the Gaussian analysis of the scattered lightintensity profile.

Surface Tension

The surface tension is a value measured at a temperature between 23.0°C. and 26.0° C. by the air bubble pressure method using a surfacetensiometer SITA Pro Line T15 (SITA Messtechnik Co, Dresden GE.). Thebubble lifetime used is 10 seconds and this is the time between thegeneration of a new air-liquid interface (at the tip of a capillaryimmersed into the ink liquid) until the maximum bubble pressure isreached. The maximum pressure measured is automatically recalculatedinto a surface tension value of the liquid (in mN/m) after calibrationof the device in distilled water.

Viscosity

The viscosity of (dispersion and supernatant liquid) is measured with aHaake Rheostress RS6000 operated in shear rate sweep from 0.1 to 3000l/s at 25° C. and expressed in mPa·s. The instrument is equipped with acone/plate geometry type C60/1° and the gap is set to 0.052 mm. Thereported viscosity is measured at a frequency of 3000 l/s.

Water Solubility of the Block Copolymer Dispersant

A block copolymer is defined as “water-soluble” when the block copolymerremains in solution in water at 25° C. with at least 15 wt. % of drypolymer in water during at least a week, preferably remains in solutionin water at 25° C. for at least one or more months, more preferably theweight percentage of dissolved dry polymer in water at 25° C. is atleast 20 wt. % during at least a week and most preferably the weightpercentage of dissolved dry polymer in water at 25° C. is at least 25wt. % during at least a week. The polymer dispersant solution isobtained by mixing the dried block copolymer with 100 g distilled waterfor at least 2 hours at a temperature of at least 25° C. Stirring and/orincreasing the temperature up to 60° C. may be used to accelerate thedissolution process. The time of mixing may be selected between 2 hoursand 12 hours.

In case where the dry block copolymer contains acidic repeating units inthe matrix stabilization segment, the “water-soluble” test conditionsare carried out by neutralizing all acidic functions by addingmonoethanol amine (MEA) base to water such that the pH of the polymersolution is 8.5 or above. In case where the dry block copolymer containsbasic functionality in the repeating units of the matrix stabilizationsegment, the “water-soluble” state test conditions are carried out byneutralizing all basic functions by adding HCl to water such that the pHof the polymer solution is 5.5 or below.

Assessment Methodology Stability of Dispersions

The dispersion stability of the pigment dispersion was tested in veryharsh conditions. The dispersions were stored at elevated temperature of80° C. for 7 days after having added diethylene glycol monobutyl ether(DEGMBE) as an organic solvent for disturbing the pigment dispersionstability.

A closed glass vial with 5 g of dispersion, 1.5 g of DEGMBE and 8.5 g ofwater was used. The pigment dispersion has 15 wt-% pigment relative tothe total weight of the pigment dispersion. The amount of pigment in thetest is 15 wt-% x 5 [g]/15 [g]=5 wt-% relative to the total weight ofthe composition. The amount of DEGMBE is 1.5/15=10 wt-% relative to thetotal weight of the composition. Particle size is measured before andafter the heat treatment. The stability is considered good when the dv50after the heat treatment is smaller than 1.10 times the dv50 before theheat treatment.

Grinding Performance of Dispersing Agents

Grinding performance of dispersing agents is determined by the particlesize that can be obtained after grinding. Good grinding performance isreached dv50<175 nm. When the grinding performance is not withinspecification no stability test was performed.

The Hansen Solubility Parameters

The Hansen Solubility parameters according to the invention arecalculated according to Y-MB methodology using HSPiP software version5.2.03 and expressed in cal^(1/2) cm^(−3/2).

Examples of the Hansen Solubility parameters of repeating units R1 andR2 are shown in Table 3.1 and 3.2.

TABLE 3.1 Examples of less hydrophobic repeating units R1 comprising analkoxyether group. The values are expressed in [cal^(1/2) cm^(−3/2)]Repeating unit R1 (without vinyl bond) δ(polar + Monomer name [in SMILESnotation] δ(polar) δ(hydrogen) hydrogen) MethylpolypropyleneCOCCCOCCCOCCCOCCCOCCCOC(═O)CC 6.4 5.2 8.2 glycol acrylatemethylpolyethyleneglycol COCCOCCOCCOCCOCCOC(═O)CC 5.4 7.4 9.2 acrylateEthoxyethoxy ethyl CCOCCOCCOC(═O)CC 5.4 6.6 8.5 acrylate2-[[(Butylamino)carbonyl] CCCCNC(═O)OCCOC(═O)CC 8.1 7.8 11.25 oxy]ethylacrylate minimum 5.2 5.2 8.1

Table 3.1 shows the polar bonding value δ(polar) of R1 and the hydrogenbonding value δ(hydrogen) of R1 and the Hansen Solubility Parametervalue δ(polar+hydrogen)_(R1), being the sum of the polar bonding valueof R1 and the hydrogen bonding value of R1. The values are expressed in[cal^(1/2) cm^(−3/2)].

The sum of the polar bonding value of a repeating unit and the hydrogenbonding value of repeating unit is defined as the square root of the sumof the square of the polar bonding value of the repeating unit and thesquare of the hydrogen bonding value of the repeating unit:δ(polar+hydrogen)=√[δ(polar)²+δ(hydrogen)²].

TABLE 3.2 Examples of ‘hydrophobic’ repeating units R2. The values areexpressed in [cal^(1/2) cm^(−3/2)] Monomer Repeating unit R2 (withoutvinyl bond) δ(polar + name [in SMILES notation] δ(polar) δ(hydrogen)hydrogen) biphenyl CCC(═O)OC1═CC═CC═C1C2═CC═CC═C2 3.3 4.3 5.4 acrylatestearylacrylate CCCCCCCCCCCCCCCCCCCCCCCCCCOC(═O)C═ 1.5 2 2.5benzylacrylate CCC(═O)OCC1═CC═CC═C1 4 5.5 6.8 ethylhexylCCCCC(CC)COC(═O)CC 3 4.1 5.1 acrylate isodecyl CC(C)CCCCCCCOC(═O)CC 2.83.3 4.3 acrylate styrene CCC1═CC═CC═C1 2.3 3 3.8 n-butyl CCCCOC(═O)CC4.3 5.6 7.1 acrylate phenylacrylate CCC(═O)OC1═CC═CC═C1 4.3 5.7 7.1maximum 4.3 5.7 7.1

Table 3.2 shows the polar bonding value δ(polar) of R2 and the hydrogenbonding value δ(hydrogen) of R2 and the Hansen Solubility Parametervalue δ(polar+hydrogen)_(R2), being the sum of the polar bonding valueof R2 and the hydrogen bonding value of R2. The values are expressed in[cal^(1/2) cm^(−3/2)].

Results

Several block copolymeric dispersants were prepared according to Table4:

TABLE 4 composition of exemplary block copolymeric dispersantsDispersant # Chemical Formula Description DA1 NaA₁₅-BnA₃₀ matrixstabilization segment of 15 repeating units of sodium salt of acrylicacid and anchoring segment of 30 repeating units of benzylacrylate DA2(BnA₂₀/EOEOEA₂₀)—NaA₂₅ matrix stabilization segment of 25 repeatingunits of sodium salt of acrylic acid and anchoring segment of 20repeating units of 2-(2- Ethoxyethoxy)ethyl acrylate and 20 units ofbenzylacrylate DA3 NaA₂₅-BnA₄₀ matrix stabilization segment of 25repeating units of sodium salt of acrylic acid and anchoring segment of40 repeating units of benzylacrylate DA4 (BnA₃₀/EOEOEA₁₀)—NaA₁₅ matrixstabilization segment of 15 repeating units of sodium salt of acrylicacid and anchoring segment of 10 repeating units of 2-(2-Ethoxyethoxy)ethyl acrylate and 30 units of benzylacrylate DA5EOEOEA₃₀—NaA₂₅ matrix stabilization segment of 25 repeating units ofsodium salt of acrylic acid and anchoring segment of 30 repeating unitsof 2-(2- Ethoxyethoxy)ethyl acrylate DA6 EOEOEA₃₀—NaA₁₄ matrixstabilization segment of 14 repeating units of sodium salt of acrylicacid and anchoring segment of 30 repeating units of 2-(2-Ethoxyethoxy)ethyl acrylate DA7 (BnA₃₀/BACA₁₀)—NaA₂₀ matrixstabilization segment of 20 repeating units of sodium salt of acrylicacid and anchoring segment of 10 repeating units of 2-[[(Butylamino)carbonyl]oxy]ethyl acrylate and 30 units of benzylacrylateDA8 (BnA₂₀/BACA₁₀)—NaA₂₀ matrix stabilization segment of 20 repeatingunits of sodium salt of acrylic acid and anchoring segment of 10repeating units of 2- [[(Butylamino)carbonyl]oxy]ethyl acrylate and 20units of benzylacrylate

Different pigment dispersion were prepared (Table 5) using the blockcopolymeric dispersants mentioned in Table 4 according to thecomposition mentioned in table 2. The pigment dispersions of examples1-10 contained 15 wt % dispersant and the pigment/dispersant weightratio is 1, resulting in 30 wt % pigment plus dispersant in the pigmentdispersion. The pigment dispersions contained water as aqueous carrierduring the grinding experiments and no water soluble organic solvents.Example 11 and 12 contained 7.5 wt % dispersant and thepigment/dispersant weight ratio is 1:0.5, resulting in 15 wt % pigmentplus dispersant in the pigment dispersion.

TABLE 5 evaluation pigment stability of several pigment dispersions PSDHeat [dv50] in nm treatment Example inv/ Pigment Dispersant after HeatGrinding stability # comp [color] # milling treatment [evaluation][evaluation] 1 inv c DA2 152 137 V V 2 inv m DA4 153 117 V V 3 inv m1DA4 134 110 V V 4 inv k DA2 146 158 V V 5 comp c DA1 185 — X — 6 comp mDA3 192 — X — 7 comp k DA3 233 — X — 8 comp m DA5 124 211 V X 9 comp mDA6 113 244 V X 10 comp k DA5 119 646 V X 11 inv k DA7 113 120 V V 12inv m1 DA8 136 114 V V

Notes: Pigment Selection:

-   -   C: PB15:3 from Clariant: PV Fast Blue BG    -   M: PR122 from Clariant: Inkjet Magenta E02    -   M1: PR122 from BASF: Cinquasia magenta D 4450J    -   K: PBk7 from Omsk: N220FA

Evaluation Stability:

-   -   V: Ok    -   X: not Ok

Grinding performance was considered OK (V) when the dv50<175 nm. Theheat treatment stability is considered good when the dv50 after the heattreatment is smaller than 1.10 times the dv50 before the heat treatment.

Equivalent good grinding results and stability results are obtained asshown in Table (5) for Example 1-4 using dispersants DA2, DA4 which areneutralized with triethanol amine or with monoethanol amine instead ofusing a sodium salt. Thereby it is demonstrated that the advantageousproperties of these dispersants do not depend on the type of counterion.

From the examples in Table 5 it can be concluded that extremely stablepigment dispersions can be obtained in a water carrier without watersoluble organic solvents for the pigment dispersions 1-4 and 11-12having a block copolymeric dispersant comprising in its anchoringsegment a hydrophobic repeating unit R2 and a repeating unit R1 having aethoxy glycol group. The comparison examples 5-10 show that a blockcopolymeric dispersant having in its anchoring segment only ahydrophobic repeating unit R2, comprising benzyl, or a block copolymericdispersant comprising in its anchoring segment only a repeating unit R1having a ethoxy glycol group do not provide a combination of goodmilling behavior and a good thermal stability of the dispersion.

With the pigment dispersions of Examples 1 to 4 inkjet inks wereprepared according to Table 6.

TABLE 6 inkjet ink compositions ink 1 ink 2 ink 3 ink 4 ink 5 ink 6pigment ex 1 ex 2 ex 3 ex 4 ex 1 ex 11 dispersion conc pigment 20 40 4035 20 35 dispersion glycerol 20 18 18 18 18 18 1-2 propanediol 10 9 9 99 9 diethylenglycol 3 3 3 3 3 3 monobutylether surfynol 465 0.9 0.9 0.90.9 0.9 0.9 dynol 960 1.8 1.8 1.8 1.8 1.8 1.8 joncryl J8050E 0 0 0 0 7.50 nuosept 22 0.003 0.003 0.003 0.003 0.003 0.003 water bal- bal- bal-bal- bal- bal- ance ance ance ance ance ance

All the inks have a viscosity between 4-7 mPa·s and a surface tensionmeasured with a Sita bubble tensiometer after 10 sec between 20 and 27mN/m.

With the inks an excellent jet quality and image quality was observedusing a KJ4B AQ printhead from Kyocera at a printing speed of 1 m/s oncoated and uncoated paper substrates.

Example 5 demonstrates that when using a binder resin (Joncryl J8050E)the inkjet ink remains stable. The binder resin Joncryl J8050E improvesthe adhesion of the pigment to various paper and filmic substrates.

1. Inkjet ink for forming an image on a substrate, the inkjet inkcomprising: a pigment P, a block copolymer dispersant D for dispersingthe pigment P, and an aqueous carrier; wherein said block copolymerdispersant D comprises an anchoring segment A for anchoring to thepigment P, wherein the block copolymer dispersant D additionallycomprises a matrix stabilization segment M for aqueous phasestabilization of the pigment, wherein the anchoring segment A comprisesa repeating unit R1 and a repeating unit R2, different from R1, whereinthe repeating unit R1 is less hydrophobic than the repeating unit R2,wherein the repeating unit R1 comprises a (poly)alkylene oxide coupledto a terminal group via a direct bond, a —C—O—C— ether bond or a—C—O—(C═O)—N— urethane bond, wherein the terminal group is selected froman alkyl group, an aryl group and combinations thereof and wherein theweight ratio between the pigment P and the block copolymer dispersant Dis between 0.05 and 2.0.
 2. The ink according to claim 1, wherein theterminal group is an alkyl group.
 3. The ink according to claim 1,wherein the repeating unit R1 comprises a polyalkylene oxide group, thepolyalkylene oxide group preferably comprising glycol unitsindependently selected from ethylene glycol and propylene glycol.
 4. Theink according to claim 1, wherein the repeating unit R1 has a HansenSolubility Parameter value δ(polar+hydrogen)_(R1), whereinδ(polar+hydrogen)_(R1)>8.0 cal^(1/2) cm^(−3/2), wherein the HansenSolubility Parameter value δ(polar+hydrogen) is defined as√[δ(polar)²+δ(hydrogen)²].
 5. The ink according to claim 1, wherein therepeating unit R1 is a non-ionic repeating unit.
 6. The ink according toclaim 1, wherein the polar bonding value of R1: δ(polar)_(R1)>5.0cal^(1/2) cm^(−3/2).
 7. The ink according to claim 1, wherein therepeating unit R2 of the anchoring segment A is formed using ahydrophobic monomer Mn₂ selected from the group consisting of amethacrylate, an acrylate, and vinyl monomers, and the repeating unit R1of the anchoring segment A is formed using a non-ionic less hydrophobicmonomer Mn₁ which is selected from the group of a methacrylate, anacrylate, and vinyl monomers, wherein preferably the monomer Mn1contains an alkoxyether terminal group; wherein preferably thehydrophobic monomer Mn₂ is at least one of benzyl methacrylate, butylmethacrylate, methyl methacrylate, ethyl methacrylate, propylmethacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octylmethacrylate, lauryl methacrylate, stearyl methacrylate, p-tolylmethacrylate, sorbyl methacrylate, benzyl acrylate, butyl acrylate,methyl acrylate, ethyl acrylate, propyl acrylate, hexyl acrylate,2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, stearylacrylate, p-tolyl acrylate, sorbyl acrylate, and mixtures thereof and/orwherein the non-ionic less hydrophobic monomer Mill is at least one oftri(ethylene glycol) methyl ether acrylate, 2-(2ethoxyethoxy)ethylacrylate (EOEOEA), ethylene glycol methyl ether acrylate, 2-ethoxyethylacrylate, di(ethylene glycol) methyl ether acrylate, ethylene glycolmethyl ether methacrylate, 2-ethoxyethyl methacrylate, di(ethyleneglycol) methyl ether methacrylate, tri(ethylene glycol) methyl ethermethacrylate, 2-[[(butylamino)carbonyl]oxy]ethyl acrylate, and mixturesthereof. 8-11. (canceled)
 12. The ink according to claim 1, wherein thematrix stabilization segment M is formed using at least one monomer Mn₃for obtaining an ionic hydrophilic repeating unit R3, respectively, theionic hydrophilic repeating unit R3 optionally containing a neutralizedacid group, neutralized basic group or other ionic functionality such asquaternary ammonium group; wherein preferably the at least one monomerMn₃ is selected from the group consisting of methacrylic acid, acrylicacid, maleic acid, maleic acid monoester, itaconic acid, itaconic acidmonoester, crotonic acid, crotonic acid monoester,N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate,N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate,t-butylaminoethyl methacrylate, t-butylaminoethyl acrylate, and mixturesthereof and/or wherein preferably the repeating unit R3 comprises anionic moiety. 13-14. (canceled)
 15. The ink according to claim 1,wherein the repeating units R1, R2 of the anchoring segment A do nothave an ionic group.
 16. The ink according to claim 1, wherein theanchoring segment A has a number of repeating units n and wherein thesum of the repeating units R1 and the repeating units R2 is at least 50number-% of the total number of repeating units n, preferably at least80 number-% of the total number of repeating units n; and/or wherein theratio between the number of repeating units R1 (n1) and the number ofrepeating units R2 (n2) is between 0.05 and 20, preferably between 0.2and
 5. 17. The ink according to claim 1, wherein the block copolymerdispersant D is selected from a diblock copolymer and a triblockcopolymer, preferably wherein the block copolymer dispersant D has atleast three blocks and the matrix stabilization segment M comprises amatrix stabilization block M1, which is arranged between the firstanchoring block A1 and the second anchoring block A2.
 18. The inkaccording to claim 1, wherein the anchoring segment A of the blockcopolymer dispersant D comprises a first anchoring block A1, comprisingthe repeating unit R1, and a second anchoring block A2, comprising therepeating unit R2.
 19. The ink according to claim 18, wherein the blockcopolymer dispersant D has at least three blocks and the matrixstabilization segment M comprises a matrix stabilization block M1, whichis arranged between the first anchoring block A 1 and the secondanchoring block A2.
 20. An aqueous pigment dispersion for forming aninkjet ink, the pigment dispersion comprising a pigment P, a blockcopolymer dispersant D for dispersing the pigment P, and an aqueouscarrier; wherein said block copolymer dispersant D comprises ananchoring segment A for anchoring to the pigment P, wherein the blockcopolymer dispersant additionally comprises a matrix stabilizationsegment M for aqueous phase stabilization of the pigment, wherein theanchoring segment A comprises a repeating unit R1 and a repeating unitR2, different from R1, wherein the repeating unit R1 is less hydrophobicthan the repeating unit R2, wherein the repeating unit R1 comprises a(poly)alkylene oxide coupled to a terminal group via a direct bond, a—C—O—C— ether bond or a —C—O—(C═O)—N— urethane bond, wherein theterminal group is selected from an alkyl group, an aryl group andcombinations thereof, and wherein the aqueous carrier contains water,and optionally a total amount of water soluble organic solvent, which isless than 5 wt %, preferably less than 2 wt %, of the total weight ofthe aqueous carrier, wherein preferably the repeating unit R1 is anon-ionic repeating unit.
 21. (canceled)
 22. The aqueous pigmentdispersion according to claim 20, wherein the repeating unit R1comprises a polyalkylene oxide group, the polyalkylene oxide grouppreferably comprising glycol units independently selected from ethyleneglycol and propylene glycol.
 23. The aqueous pigment dispersionaccording to claim 20, wherein the repeating unit R1 has a HansenSolubility Parameter value δ(polar+hydrogen)_(R1), whereinδ(polar+hydrogen)_(R1)>8.0 cal^(1/2) cm^(−3/2), wherein the HansenSolubility Parameter value δ(polar+hydrogen) is defined as√[δ(polar)²+δ(hydrogen)²].
 24. The aqueous pigment dispersion accordingto claim 20, wherein the amount of pigment P in the pigment dispersionis in the range of 10-80 wt-% based on weight of the pigment dispersion.25. The aqueous pigment dispersion according to claim 20, wherein theamount of water in the aqueous carrier is at least 50 wt.-%, preferablyat least 80 wt.-%, more preferably at least 95 wt.-%, of the totalweight of the aqueous carrier. 26-29. (canceled)
 30. An inkjet ink forforming an image on a substrate, the inkjet ink comprising: a pigment P,a block copolymer dispersant D for dispersing the pigment P, and anaqueous carrier; wherein the block copolymer dispersant D comprises ananchoring segment A for anchoring to the pigment P, wherein the blockcopolymer dispersant D additionally comprises a matrix stabilizationsegment M for aqueous phase stabilization of the pigment, wherein theanchoring segment A comprises a repeating unit R1 and a repeating unitR2, different from R1, wherein the repeating unit R1 is less hydrophobicthan the repeating unit R2, wherein the repeating unit R1 comprises a(poly)alkylene oxide coupled to a terminal group via a direct bond, a—C—O—C— ether bond or a —C—O—(C═O)—N— urethane bond, wherein theterminal group is selected from an alkyl group, an aryl group andcombinations thereof, and wherein the weight ratio between the pigment Pand the block copolymer dispersant D is between 0.1 and 1.0.